1. Field of the Invention
The present invention relates to a sheet processing apparatus having a conveying guide for guiding a sheet.
2. Description of the Related Art
As an apparatus which processes a sheet, there is an image forming apparatus which forms an image on a sheet. There is an image forming apparatus in which a two-sided unit is mounted on a side surface or an upper surface of an apparatus body so that images can be formed on both sides of a sheet. An optional paper feed apparatus which feeds sheets to the apparatus body proceeds toward commercialization.
User's needs for downsizing the image forming apparatus have grown. It is required to bring a plurality of conveying paths such as a sheet conveying path in the two-sided unit and a paper feed sheet conveying path from the paper feed apparatus adjacent to each other, thereby downsizing the apparatus. Further, it is necessary to secure a sufficient operation space for jam recovery for a user.
In an area of the image forming apparatus body where a plurality of conveying paths such as a conveying path from a sheet paper feed apparatus, a conveying path from the two-sided unit and an optional paper feed sheet conveying path merge with each other, a plurality of conveying guides and conveying rollers are closely provided. It is both important to carry out the jam recovery operation and to secure the space.
In a copier disclosed in Japanese Patent Application Laid-Open No. 2005-31377, an opening/closing cover is turnably mounted on a copier body. A movable paper guide is movably mounted on the copier body. If the opening/closing cover is opened, the movable paper guide is opened. However, since the movable paper guide is mounted on the copier body, the opening degree of the conveying path caused by movement of the movable paper guide is small and thus, the operability of the jam recovery is poor. In an area where the conveying path is largely bent and a plurality of conveying paths exist in a narrow space, the position precision of a sheet guide is important. In the copier disclosed in Japanese Patent Application Laid-Open No. 2005-31377, since the movable paper guide is mounted on the copier body, it is difficult to secure the position precision of the conveying roller and the movable paper guide of the opening/closing cover.
According to a structure disclosed in Japanese Patent Application Laid-Open No. 2006-259449, two conveying paths, i.e., a sheet conveying path passing through an image forming portion and a sheet conveying path of the two-sided unit are simultaneously opened by a user's operation for turning the two-sided unit (door) with respect to the apparatus body. Here, if the two-sided unit (door) is turned with respect to the apparatus body to open the conveying path from the sheet paper feed apparatus of the apparatus body, roller nips of a pair of registration roller and a pair of rollers of the two-sided unit are released. By releasing the roller nips, processing operability of sheets remaining in the sheet conveying path is enhanced.
However, if the roller nips of the pair of registration roller and the pair of rollers of the two-sided unit are released, although the processing operability of remaining sheets is enhanced, the following problems come up.
It is difficult to align a pair of rollers such as registration rollers. If the rollers are not aligned, a sheet is skew fed, and forming precision of an image is deteriorated.
Generally, high nip pressure is set for a pair of rollers. When thick paper sheets of 200 g/mm or more are conveyed, for example, high nip pressure is required so that sheet conveying speed is not reduced with respect to the image forming portion. For a pair of rollers which convey sheets in a bent sheet conveying path, it is necessary to set a nip pressure as high as 1 kgf to 2 kgf so that the rollers and the sheet do not slip due to conveying resistance of the sheet.
If a high nip pressure is set for a pair of rollers, a user must operate a user door against the nip pressure. Thus, the operability of the user's door is deteriorated. If a high nip pressure is set in the pair of rollers, a strong casing is required to handle the nip pressure. Thus, if a structure in which the pair of rollers are held by resin material, countermeasures against deformation such as creep are required. In the case of a structure in which the nip of a pair of rollers is released as a door is turned as in Japanese Patent Application Laid-Open No. 2006-259449, it is difficult to secure the strength.
A structure in which nip of a pair of rollers is not released even if a door is opened or closed can be conceived. However, if the nip of the pair of rollers is not released even when the door is turned, the following problems come up.
When sheets remain in a state where the sheets are nipped by a plurality of pairs of rollers, the conveying guide comes into contact with the remaining sheets if a user opens the door. If the user further opens the door, the conveying guide tears the sheets. Further, there is a fear that the conveying guide is damaged by the sheets.
This problem will be described using FIG. 13 which is a sectional view of a sheet conveying portion near a door. FIG. 13 illustrates a state where a door 150 having a conveying guide 139 is opened. The door 150 is opened without releasing the roller nips of the pair of rollers 114 and the pair of two-sided rollers 135. The remaining sheet S is nipped between the pair of rollers 114 and the pair of two-sided rollers 135. When the door 150 is opened, the conveying guide 139 disposed on the door 150 turns toward the sheet nipped (in the direction of the arrow A) by the pair of rollers 114 and the pair of two-sided rollers 135. Therefore, there is a fear that the sheet S is pulled by the tip end 139a of the conveying guide 139 by the turning motion of the door 150 and is torn, and a flake of the sheet remains in the apparatus. There is a fear that the tip end 139a of the conveying guide 139 is damaged by the sheet. Further, tension of the sheet nipped between the two roller nips becomes a resistance when the door 150 turns, and the operability is deteriorated.
To solve the above problem, it is conceived that a plurality of user access doors corresponding to the plurality of conveying paths are provided, but a user can not easily find a door which should be opened at the time of jam recovery, and the operability is poor.